The American "Mother of All Bombs" has returned to the forefront, after President Donald Trump hinted in mid-October at the possibility of using it in a war on Iran, as part of options being considered by the US military.
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The bomb, developed in 2003 and bearing the military name "GBU-43/B, MOAB," was used only once, on April 13, 2017, when the United States used it in the Achin region of Afghanistan, causing an exceptional explosion. Its sound signature traveled about 249 kilometers, enabling researchers to detect that signature inside Pakistan and use it to estimate the bomb's explosive power.
This bomb is about 9.1 meters long, and is designed to be dropped from a C-130 military transport aircraft. It uses a global positioning system along with an inertial navigation system to guide it towards the target.
Unlike bombs designed to penetrate deep fortifications, the "Mother of All Bombs" explodes in the air before reaching the Earth's surface, causing the explosion's energy and pressure wave to spread in the surrounding air, thus distributing the effects of the explosion over a wider area instead of concentrating them at a single point of impact.
It is known that explosions do not produce a single sound, but rather release waves that differ in their frequencies and characteristics. Some of these waves fall within the range that the human ear can hear, while the frequency of some others drops to less than 20 Hz, which is known as "infrasound waves" that the human ear cannot hear under normal conditions, but they remain detectable using specialized devices.
When a bomb explodes, the hot gases expand at an enormous speed, pushing against the surrounding air and generating pressure changes that spread far from the source of the explosion. Depending on weather conditions, these waves can travel long distances, even when the explosion is no longer audible to humans. This is the idea the researchers based their work on: what the ear cannot hear, measuring devices may be able to detect and analyze.
In their study, the researchers relied on a seismic and acoustic monitoring station in Pakistan located about 249 kilometers from the blast site. They reviewed the information recorded by the station and confirmed the arrival of the infrasonic wave, and analyzed its physical properties to find out what it could reveal about the explosion that produced it.
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